1. Field of the Invention
The present invention relates to a process and an apparatus for amino acid fermentation employing bacterial cells in which the fermentation solution containing bacterial cells is recirculated for use in continuous amino acid fermentation.
2. Description of the Background
Methods, such as the additional feeding of sugar or the like and the supply of sufficient oxygen, as demanded by bacterial cells, have been proposed for improving the fermentative production of an amino acid such as glutamic acid. None of these methods, however, have resulted in any greatly increased production of amino acids, since a decrease of cell density and a lowering in the capacity for amino acid production occurs during the latter part of the fermentation process.
A process has been proposed which is a continuous culturing process in which basically a portion of the fermentation solution is withdrawn from a fermenter, the withdrawn solution is then separated into a solution containing bacterial cells and a solution which does not contain bacterial cells in a cell separator, and the former solution is recycled to the fermenter (Japanese Patent Application Laid-Open No. 48394/1987). The continuous culturing process has exhibited a very high level of productivity during its experimental stage in comparison to other known processes. However, it has been more difficult to carry out this process successfully on a large scale, in comparison to experimental size operations which are carried out on a smaller scale and which do not present any significant problem.
The known continuous culture process essentially calls for circulation of the fermentation solution from a fermenter to a cell separator and from the cell separator to the fermenter. Obviously, various kinds of pumps must be used to achieve this circulation. One of the pumps is a tube pump. However, no satisfactory tube pump has been available which can smoothly circulate a large amount of the fermentation solution when the process is carried out on a large commercial scale, even though a tube pump exists which is useful when the process is carried out on a small experimental scale.
Amino acid fermentation, such as glutamic acid or lysine fermentation, is aerobic fermentation which calls for aeration and agitation, and yields a fermentation solution containing a large amount of bubbles. These bubbles cause cavitation in any pump which is used other than the tube pump and prevent the smooth circulation of the fermentation solution. Accordingly, it has hitherto been impossible to carry out the continuous culturing process successfully on a commercial basis, because there has not been any alternative but to use a pump which is other than a tube pump, and therefore the problem of cavitation by bubbles is encountered.
The bubbles create a great resistance to the circulation of the solution in a pipeline, and also lower the performance of the cell separator if it is of the centrifugal type. Accordingly, a need continues to exist for an improved continuous process for amino acid fermentation.